A method for detecting combustion misfires is already known from U.S. Pat. No. 5,955,663 wherein an index for the rough running of the internal combustion engine is formed and is compared to a threshold value. The threshold value is dependent upon the load of the engine and exceeding the threshold value is evaluated as a misfire. The load, that is, essentially the charge of the cylinder with air influences the rough running significantly. With the torque, which increases with increasing load, the acceleration forces acting on the crankshaft increase and thereby effect an increasing rough running.
The task of the invention comprises a further improvement of the detection quality of the combustion misfires.
The solution considers that the rough running of the engine is dependent upon the torque of the engine for a regular combustion. In addition to load, which is essentially defined by the cylinder charge with air, the ignition angle and the air/fuel ratio of the cylinder charge also influence the torque resulting from the combustion of the cylinder charge and thereby the rough running which is to be expected under regular conditions.
The consideration of the ignition angle in accordance with the invention and/or of the air/fuel ratio of the cylinder charge in the determination of the threshold value or in the formation of an index for the rough running of the engine and/or for the activation/deactivation of the misfire detection permits a lesser spacing of threshold value and rough running values under regular conditions and therefore a more sensitive detection of the non-regular conditions, that is, especially of misfires.
The consideration in accordance with the invention of the ignition angle in modern internal combustion engine controls is of special advantage. The combustion engine controls use also the ignition angle as an actuating variable for realizing a requested torque in addition to the cylinder charge.
In contrast to other internal combustion engine controls, the comparatively rigid coupling of the ignition angle to load and rpm is unnecessary in these modern engine controls. The reduced dependency of the ignition angle on these quantities increases the inherent influence of the ignition angle on the torque and therefore the advantageous effects of the invention.
The composition of the air/fuel mixture additionally influences the torque. A further increase of the accuracy therefore results from a consideration of the composition of the air/fuel mixture.
In engines having gasoline direct injection, operating conditions are conceivable wherein the desired torque for a pregiven air charge and fixed optimal ignition angle is adjusted via the quality of the air/fuel mixture, that is, via the lambda value of the mixture.
In such operating conditions, it is therefore not the ignition angle but the composition of the air/fuel mixture which is the decisive quantity to be considered in accordance with the invention.
Furthermore, a supplemental consideration of the condition of a torque converter bridging clutch in vehicles having automatic transmissions is advantageous.
The drive train defines a system capable of oscillation. Depending upon whether the clutch is open or closed, there is also a different effect via attenuating or exciting influences on the rough running values of the engine. In this way, the disturbance spacing can be influenced, that is, the spacing of the rough running values under the influence of misfires from the rough-running values for regular combustion.
The supplemental consideration of the converter bridge coupling permits also here an optimization of the disturbance spacing.
The consideration of the ignition angle for the activation/deactivation of the combustion misfire detection leads to a further increased reliability of the combustion misfire detection.